Faux LED Scroller Using Phosphorescence

Hackaday reader [BGR] wrote in to share a video he put together showing off a cool “poor man’s LED scroller” that he built. Rather than build a huge array of LEDs, spending tons of time time wiring and programming, he decided to use only a handful of LEDs on a moving display instead.

The scroller is built upon a PIC16F887 microcontroller which resides on an EasyPIC6 dev board he borrowed for the project. The PIC controls a strip of eight bright white LEDs, which are used to write text on a long strip of phosphorescent paper that can be found at many printing supply outfits. The paper’s dispensing mechanism was cobbled together with parts from several sources, including a laser printer and VCR.

When he wants to display a message, he inputs text into a flash application he wrote. The app sends the LED byte values to his scroller via a separate serial proxy that talks to the pic over his computer’s COM port.

The effect is pretty slick, looking similar to a slow-moving diffused LED scroller. The messages disappear after about 5 minutes in a pitch black room, which is perfect, since he originally intended to use the device for displaying Twitter updates. He is already considering a second revision of the project, which he wants to mount on the wall – sounds great to us!

Be sure to swing by YouTube to see the video, or continue reading to watch it here.

if he made a grid to block light around each pixel he certianly could scale up the resolution. using super bright as heck UV led’s you could then do insane intensity bursts that allows the strip to run faster for eve more fun!

I’ve been looking for the phosphor paper to do exactly this, but for a slightly different purpose. Can someone give me a source for relatively large pieces like this please?

Also it would be ideal if the paper was zinc sulfide based, not strontium aluminate. Zinc sulfide can be erased easily with IR light to quench the phosphorescence… I actually built a little testing source I carry with me, one UV LED one IR one to test phosphors I find in the hope of stumbling on exactly what I need.

This also works with the SMD 395nm UV 0603 LED’s available on ebay and elsewhere.

These can be soldered onto a fragment of pcb saved from a broken PCMCIA edge connector PCB if you can’t be bothered to make a board :-)

I did have a thought, drill a grid of 0.2mm holes, mount the SMD LEDs at a 45 degree angle inside a double layer board, solder them in place with a solder ball at each end then you have a very compact assemmbly capable of mounting on a suitable carrier unit.

If anyone makes some use of this idea, paypal the cost of a beer to the usual address :-)

@Alan Yates You could always have a look at the DIY stores, sometimes you can get glowing paint there.

Or you could make some yourself, see Jeri’s work on DIY EL phosphors using zinc acetate and thiourea.
The secret to long persistence is to mix in a bit of copper and chlorine dopant in the form of Losalt… or use silver paint saved from old defunct PC keyboards to make ZnS:Ag “expensive” alpha scintillator that normally costs around £19 for 500mg.

This is awesome..
I have wanted to build a external closed captioning device, but the number of LEDs needed to provide the information at the same pace as the dialog is ridiculous.
This wouldn’t quite work for that application as it is a little too persistent.
What Alan was talking about could work though, since you could erase the old dialog.

Regarding the resolution capability of the paper – it’s pretty decent, you could write text that is as small as ~1cm (0.5inch) in height. You could make monochrome pictures with it, if you put it against a computer or phone display it transfers the picture but it’s a little blurred, and it’s actuated only by the blue component, red and green do absolutely nothing (I used white leds but blue ones would perform exactly the same, and UV ones even better).

I was originally planning to mix up the phosphorescent powder and apply it onto fabric or paper, but when I went to buy it I found they also sell this ready “paper” by meter that was perfect for this because it’s crap and fades after 2 minutes (it’s actually more like a 1mm thick plastic-rubber than paper, with adhesive back side, and it stretches a little so that gave me some problems with the belt).

I originally planned to have a long zig-zag belt, but this thing is expensive! One square meter is around $70. But it turns out it fades very quickly in the first few seconds, so by the time the belt makes one revolution it’s already faded enough for new text to overwrite it and be perfectly clear.

Update:- had a look here and no sign of glow in the dark paper.
Looks like I’ll have to order some, ideally it needs to be glowing acetate (perhaps I can do some chemistry voodoo and make my own!) so it works for the intended application which is a hack to a broken scrolling fish tank which mounts on the wall.

So far so good, I have determined that for half decent resolution 100 0603 or 0805 LEDs will be needed.

This is cool!
Another place to get film like this is sign shops, you can get rolls A3 width and 20 metres long.
I’ve tried this on a drum mounted up in an Epson printer, with 1 LED where the print head was.
Origionaly it was to check ATP satelite images from NOAA and Meteor satelites.

WE found if you put negatives or slides on phosphoresent film, then “hit” it with a flash gun, it transfers a very sharp image.

@Tweeks: yes you could get a sharper characters, but not really crisp, at least with this material that I have, because this one has thickness and light scatters on the inside so there’s a blurry edge that’s around 2mm wide no matter how sharp your light source is.

@M4CGYV3R: Flash app connects to a socket that’s being listened by a serial proxy utility that relays data from socket to COM port, so it’s really simple actually. No Java/ASM/C on the client side.

@YS, @bothersaidpooh: you’ll probably have to order, I was pretty damn lucky they had this, I entered the shop planning to buy powder to mix with something (I didn’t have a clue what but I knew it had to be something that doesn’t block UV). When you find it don’t be surprised if the price is around $80 per square meter, it’s expensive.

@transistorman, @Alan Yates: thanks for the IR erasing tip, I didn’t know that. I just tried it an it works :)

Yeah, this was in “New Scientist” way back when.
In fact it is a demonstration of quantum mechanics, because the phosphor behaves nonclasically.

It works because the luminous centre stores energy by the outer electron being knocked into a high orbital. As it decays back to the ground state it emits a characteristic photon of light, giving (in this case) green for ZnS:Cu

Because this excited state is affected by radiation, infrared of the correct wavelength can act like a sound wave on a tuning fork and make it “vibrate” more. This causes the electron to get perturbed and knocked out of its excited state and decay far sooner than normal, so you can see a “green flash” as it decays.

This same effect is analogous to radioactive decay, in fact the typical decay graph resembles the half life graph of a radioisotope.

(Warning:- this is the “nice” explanation. For the full text go to physorg, beware, hairy math alert!!)

@Pup, no it doesen’t affect the phosphor.
I did try this, the glow seems as strong as before even though I nuked it with a NIR laser from close range and no effect at all. No brightness change whatsoever once it has recharged evenly.